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Homework Help: Calculating centripetal force when radius is unknown

  1. Jan 9, 2010 #1
    Heres the question
    "A ball with a mass of 250 g has a centripetal acceleration of 5 m/s2. What is the centripetal force acting on this ball? "

    Since radius depends on the string length I have no idea how to derive it from these 2 variables. The only formula I know for getting centripetal force is F = m * V^2 / r
  2. jcsd
  3. Jan 9, 2010 #2
    If the acceleration is already given why do you want to calculate it?
  4. Jan 9, 2010 #3


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    Science Advisor

    Precisely. Elaborating, one rewrites the equation (F=ma) in that form (F=mv^2/r) because usually one knows velocity and radius. In this case, you know neither, so why rewrite it at all? :)
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